WASHINGTON —, the Reston, Va., company fighting to deploy a satellite-terrestrial broadband network that studies conclude would interfere with GPS reception, said it can mitigate the problem by using only a portion of the radio spectrum allocated to it by the U.S. Federal Communications Commission (FCC) and dialing back the power of its ground transmissions.
“The vast majority of GPS receivers look only at that part of LightSquared’s spectrum directly adjacent to GPS,” Jeffrey Carlisle, LightSquared’s executive vice president for regulatory affairs and public policy, told a joint hearing of the House Transportation subcommittees on aviation, and Coast Guard and maritime transportation June 23. By shifting to another frequency block and transmitting at lower power, “LightSquared will address this issue for over 99 percent of the receivers currently used.”
There are between 400 million and 500 million GPS receivers active in the United States today, LightSquared estimates.
LightSquared is licensed to use two specific 10-megahertz blocks in the L-band frequency range. Carlisle said the company will configure its hybrid network to initially use only the lower of these two blocks — the one that is farthest away from frequencies that GPS receivers tune into to pick up satellite signals. He added that LightSquared would also transmit its base-station signals at 1.6 kilowatts — about one-tenth of the power permitted under the 2010 conditional waiver granted to the company by the FCC. Finally, the company would build its ground infrastructure first near metropolitan areas and expand into rural areas later.
The types of GPS receivers most prone to disruption from LightSquared base stations include those used in agriculture. Deferring construction of base stations in rural areas would give LightSquared and the GPS industry more time to figure out how to avoid disrupting the sensitive GPS receivers used in agriculture, Carlisle said.
This three-point plan is a departure from the company’s previous business model, under which LightSquared would have first used the higher of its two 10-megahertz L-Band allocations, transmitted ground signals at 15 kilowatts, and begun building base stations in rural areas immediately.
Carlisle’s testimony expanded on a LightSquared statement released June 20, in which the company acknowledged its transmissions could blank out GPS signal reception.
“Early test results indicated that one of LightSquared’s 10 megahertz blocks of frequencies poses interference to many GPS receivers,” the company said. However, “LightSquared determined that another 10-megahertz block of the spectrum did not create such an interference risk.”
A GPS-industry representative called LightSquared’s new plan impractical, asserting that even at the lower power levels, LightSquared’s ground-based transmissions would still be far more powerful than the satellite signals that have traditionally used that portion of spectrum.
“LightSquared’s proposal is sort of like running a lawnmower in a library,” said Phillip Straub, vice president of aviation engineering at GPS equipment maker Garmin International, Lenexa, Kan. Straub called on lawmakers to work toward “the rescission of the FCC’s waiver” that allowed LightSquared to offer a terrestrial-only service along with the satellite-terrestrial service.
The hearing marked the first time that LightSquared appeared before Congress to respond to a pair of technical reports that concluded the company’s planned network posed an unacceptable threat to GPS navigation signals whose applications include public safety.
The reports, released June 9, include the findings of the White House-chartered National Space-Based Positioning Navigation and Timing Systems Engineering Forum, which does technical analysis of GPS issues, and RTCA Inc., a nonprofit that advises the federal government on air-traffic management and associated technology.
There is a thread of support for LightSquared’s new plan the RTCA reports, which notes that GPS receivers aboard aircraft might be safe from distortion if LightSquared transmits only on the lower half of the 10-megahertz frequency block on which the company now plans to debut its network.
“Use of a single 5-megahertz lower channel could allow the LightSquared system to co-exist with aviation’s use of GPS,” Margaret Jenny, president of RTCA, said in prepared remarks at the hearing. The RTCA study only looked at the effect of LightSquared transmissions on GPS receivers used in aviation.
However, the RTCA report concluded that using the upper 5 megahertz of LightSquared’s favored frequency range would still interfere with aircraft GPS receivers. The company’s plan, therefore, is still incompatible with GPS use, the report concludes.
Carlisle said further study would be needed to determine whether only half of the L-band frequency block LightSquared wants to use for initial service is compatible with aviation GPS systems.
Meanwhile, LightSquared is betting that a full technical report, due to the FCC July 1, will vindicate its new business plan.
The report contains the findings of a Technical Working Group led by LightSquared and comprising industry and government experts. The report was to have been turned in June 15, but LightSquared asked for, and received, a two-week extension from the FCC.
Under its current business plan, LightSquared seeks to build a multibillion-dollar network of 36,000 base stations to augment its satellite service. The company, which has one satellite on orbit and has invested about $1 billion to date, would sell broadcast capabilities at the wholesale level.